Electrical measuring instrument.



P. MACGAHAN- ELECTRICAL MEASURING INSTRUMENT. APPLICATION F|LED JULY29, ma.

Patented June 12, 1917.

' UNITED STATES PATENT OFFICE, I

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ELEC'IBICI: MEASURING- INSTBUlb Im.

Patented June12, 1917.

Application filed July 20, ms. semi no. 751,748.

To all whom it may concern.

Be it known that I, PAUL MAcGAHan,

a citizen of the United States, and a resident of Pittsburgh, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Electrical Measuring Instruments, of which the following is a specification.

been provided that admit of adjustment of vention.

the zero position over a relatively narrow range. If the movement of the spring through a relatively narrow range did not sufficiently adjust it, the length of the spring had to be varied by moving the spring holder. This required a change in the constant of the instrument as well as delicate handling and was usually a source of trouble. In my invention, I provide means for adjusting the zero position of a spring over any range without changing the length and consequent counter-torque of the spring, and I also provide means for permitting these adjustments to be made in small increments to admit of accurate adjustment withease. I also provide means whereby the length, and thus the strength, of the s ring may be readily adjusted withoutinter ering with the action of the zero-adjusting feature. v

In the accompan in'g drawings, Figure '1 is a fragmentary p an'view of a measuring instrument wherein is embodied my invention, and Fig. 2 is a sectional view of a spring adjusting device embodying my'in- Referring to the drawings, my invention is embodied in an electrical measuring in strument having a shaft 1, a pointer 2, a spring 3 and a supporting arm 4:. The supporting arm 4 is drilled to receive a bushmg 5. and a gear wheel member 6. The

bushing 5 sup orts a pinion 7. having a slot.

8 in the to t ereof. The pinion '7 is'held in the bus ing 5 by a shaft 9 that has a shoulder 10 thereon. The gear wheel memher 6 comprises a gear wheelll that engages the inion 7, and a cylindrical sleeve or projection 12 that is internally threaded to receive a jewel screw 13that is provided with a lock'nut 14 for holding it in position. To the lower end of the sleeve 12 is attached a spring washer 15 that secures the gear wheel member 6 to the supporting. arm 4 in such a way as to prevent it from moving except when manually operated. A washer 16 is attached to the sleeve 12 to hold the spring washer 15 in place and to support the inner end 17 of the spring 3, the other end 18 of which or any intermediate point thereof is attached to an arm 19 projecting from-the shaft 1 by a screw 20.

.To adjust the spring 3, the pinion 7 is rotated by turning a. screw driver which is inserted in the slot 8. This causes the gear wheel 11 and the sleeve 12 to rotate and carry with them the washer 16 which, as

hereinbefore. stated," has attached to it the inner end of the spring 3, thus adjustingthe position of the spring 3 without changing] its length. Very accurate adjustment of the springmay be had by using my inven- -tion. A novel feature of my invention is the method of suspending the rotatable member of the instrument, the jewel screw 13 inserted in the gear wheel member. 6 serving this purpose.

Anychangein the mechanical structure, sha e, size and materials of my invention, ereinbefore described, will not depart from its scope as covered by the appended claims.

I claim as my' invention 1. In an electrical measuring instrument,

the combination with a rotatable shaft, of a spring having one end attached to the rotatable shaft, a pinion, a gear wheel in engagement with the said pinion, and means connected to the said gear wheel for restraining the same and for operatively connecting the other end of the spring thereto.

2. In an electric measurin instrumen the combination with a rotateb 0 member, 0

.a pinion, a. gear wheel having a projection and adapted to be rotated through any angle and a bearing for the rotatable member,

bearing being mounted in the gear wheel projection.

- 3. In an electrical measuring instrmnent, the combination with a rotatable member, of

a pinion, a gear wheel having a projection and adapted to engage the pinion, a jewel bearing for the rotatable member that is mounted in the gear wheel projection, and means for restraining the gear wheel in any position. v

4. In an electrical measuring instrument, the combination with a rotatable shaft, of a pointer attached to the said shaft, a projecting arm on the said shaft, a spring having one end attached to the said pro ecting arm, a pinion, a gear wheel in. engagement with the said pinion, and means'connected to the said gear wheel for restraining the same and for operatively connecting the other end of the said spring to the said gear wheel.

5. In an electrical measuring instrument, the combination with a rotatable member, of a supporting member a pinion journaled in said supporting mem r, a gear wheel having a cylindr cal projection thereon and adapted to be rotated through any angle,

tached to t said projection being journaled in the said supporting member, and a bearing for thesaid rotatable member carried by the projection on the said gear wheel. I

6. In an electrical measuring instrument, the combination with a rotatable member, of a supporting member,a pinion j ournaled in the said supporting member, a gear wheel having a cylindrical projection thereon and adapted to engage the said inion, said projection beingjournaled in t e said supporting member, a jeweled bearing for the said rotatable member, said jeweled bearing being inserted in the pro ection on the said gear wheel and a spring having one end athe said rotatable member and the other end to the projection on the said gear wheel. I

7. In an electrical measurin instrument the combination w'itha rotatab e member, of a pinion, a ear wheel having a projection and adaptexf to engage the said pinion, a bearing member for the said rotatable member that is mounted in the gear wheel projection, and a spring having one endattached .to the said rotatable member and the other end attached to the gear wheel projection. v f

8. In an electrical measurin instrument the combination with a rotata le shaft, of a spring having one end attached to the rotatable shaft, means for adjustably control- .ling the spring, and means connected to the said controlling means for restraining the same and for operatively connecting the other end of the spring to the controlling means.

9. In an electrical measuring instrument,

the combination with a rotatable shaft, of-

' controlspring to the gear wheel.

In testimony whereof, I have hereunto subscribed my name this 24th day" ofJuly 1913.

PAUL MAQGAHAN. 

